An engine produces energy by combusting a mixture of air and fuel. A gas turbine engine is one type of engine that includes a compressor, combustor, and turbine. A gaseous fuel, e.g. natural gas, is burned in the combustor and exhaust is generated that drives the turbine. The turbine, in turn, drives the compressor to direct more gas and air into the combustor.
Natural gas may be transported from a location where it is produced to a location where it is consumed by tanker ships, trucks, or trains equipped with cryogenic compartments. Such a tanker may be referred to as an LNG carrier. Since liquefied natural gas (“LNG”) takes up only a fraction (about 1/600) of the volume of natural gas in its gaseous state, natural gas is transported in the LNG carrier in a liquid state. LNG may be produced by cooling natural gas below its boiling point (about −161° Celsius at ambient atmospheric pressure), causing it to condense to a liquid. LNG may be stored in cryogenic containers at a pressure between about ambient atmospheric pressure and 250 psi in the LNG carrier.
While it is more practical to transport LNG than compressed natural gas (“CNG”) because LNG takes up a fraction of the volume of CNG, most engines require gaseous fuel for combustion. By raising the temperature of the LNG, it may be converted into its gaseous form. A substantial amount of energy is required to convert LNG into its gaseous form and it is critical to minimize the amount of energy wasted during the process. In remote applications away from utility grids, it may be difficult to find a supply of energy sufficient to support large scale conversion of LNG into CNG.
One attempt at minimizing the amount of energy wasted in converting LNG into natural gas or CNG is described in U.S. Pat. No. 7,600,396 (the '396 patent) issued to Mak on Oct. 13, 2009. In particular, the '396 patent describes a regasification plant for converting LNG into CNG by using a portion of the LNG as a coolant. LNG is pumped from a storage tank and split into a first and second portion, which are both employed as a cooling medium in first and second heat exchangers, respectively. Both portions of LNG are fed to a demethanizer, which produces demethanizer overhead product. The demethanizer overhead product is sent back to the first heat exchanger where it may then exit the plant and be sold as LNG vehicle fuel or condensed, pressurized in a pump, and vaporized in an additional series of heat exchangers. To gasify the LNG, potential heat sources include gas turbine combustion air, cooling water of a surface condenser, flue gas from a gas turbine, waste heat from combined cycle power plants, waste heat from steam turbine discharge, and ambient heat within air, seawater, or fuel gas. Some of the heated and compressed supercritical gas is then released from the plant as CNG, while some is expanded in an expander turbine to generate power. The expanded gas is then cooled in heat exchangers before combination with demethanizer overhead product.
Although the regasification plant of the '396 patent may help decrease energy wasted when converting LNG into CNG, the involved system may be limited. That is, the regasification plant of the '396 patent may still require an external source of heat or power, which may restrict the portability and extent of self-powering of the system.
The disclosed system is directed to overcoming one or more of the problems set forth above and/or elsewhere in the prior art.